The overall objective of the proposed research is to effect a major enhancement in methods for macromolecular structure analysis. Recent advances demonstrate that anomalous scattering can be used for the straightforward determination of three-dimensional structure from a single macromolecular crystal. Realization of the full potential of the new methods requires further development in instrumentation, computational procedures, and biochemistry. These developments will be pursued in the context of analyzing particular crystals structures of biological significance. The overall objective is embodied in four specific aims: (1) We propose to continue our efforts to develop the theoretical basis and computational implementation of methods for exploiting the effects of anomalous scattering, particularly in multiwavelength anomalous diffraction (MAD) studies. (2) We propose to optimize the experimental procedures for conducting MAD experiments. For the most part these experiments will be conducted at the Hughes Synchrotron Resource that we are developing at Brookhaven National Laboratory. but we will also participate in the development of beamlines at other sources. (3) We propose to devise various means for introducing suitable scattering centers into macromolecules and to study the anomalous scattering characteristics of such centers. This work will emphasize general and convenient preparative procedures and especially strong scattering effects. (4) We propose to perform the methodology development in the course of applications to macromolecular crystal structures. Biologically exciting problems motivate the development of appropriate tools, and forefront methods accelerate the solution of interesting structures. Specific plans are described for studies on several systems of considerable biological and medical significance.